In the bsp.c included in the sdk package, there are the details of messages to send to BSPLAYER.exe.
I would like to resize the window (width = 800), to move it and to hide the player. But i don't kow if there are good commands ???

If you want to resize the video window in Normal (NOT FullScreen) mode you may use BSP_IncMovWin=99 and BSP_DecMovWin=100 commands.
The problem is that you can't resize it to a predefined size, but only increment/decrement it. You should read from the movie file the MovieWindowSize and calculate the steps you have to increment the window (this only if BSplayer starts playing the movie in Original aspect ratio and with the original movie dimension).
If you want you can hide (and re-show) the BSplayer skin by sending the BSP_HideCtrl=59 command.

If the names are not so explanatory to you, you can go in the Lang folder of BSplayer, and take a look at "English.lng" file at the section [Actions]. There, are listed all the actions you can use in BSplayer (even the ones not included in the SDK).

Note that you have to decrement by 1 the values in the .lng file to match the ones used for the SendMessage calls.
Ex.:File English.lng21=PlaySDK Action BSP_Play=20